The present invention relates to generally to computer power supply systems and specifically to an improved multiple output power supply circuit.
Many server computer systems utilize multiple output power supply circuits. FIG. 1 shows a conventional multiple output power supply circuit. The circuit comprises an input voltage 10, coupled to a first capacitor 14 and a transformer 18. The transformer 18 is coupled to a first diode 12, a switch 20 and two rectifiers 70, 80. The first rectifier 70 comprises a first winding 26, a MAGAMP core 24, a second diode 30, a third diode 32, a MAGAMP Driver 38, a first inductor 40, a first freewheeling diode 42, a second capacitor 50, a first resistor 58, a second resistor 60, and a first error amplifier 62. The second rectifier 80 comprises a second winding 28, a third diode 34, an optocoupler 36, a third resistor 37, a second inductor 44, a second freewheeling diode 46, a second error amplifier 48, a third capacitor 52, a fourth resistor 54, and a fifth resistor 56.
The first rectifier 70 is coupled to the transformer 18 via the first winding 26 wherein the first winding 26 is coupled to the MAGAMP core 24 and the first freewheeling diode 42. The MAGAMP core 24 is coupled to the second diode 30 and the third diode 32 wherein the third diode 32 is coupled to the first freewheeling diode 42. The second diode 30 is coupled to the MAGAMP Driver 38 wherein the MAGAMP Driver 38 is further coupled to the first error amplifier 62. The first freewheeling diode 42 is coupled the third diode 32 and to the first inductor 40 wherein the first inductor 40 is further coupled to the second capacitor 50. The second capacitor 50 is coupled to the first resistor 58 wherein the first resistor 58 is further coupled to the second resistor 60. The first and second resistors 58, 60 are coupled to the first error amplifier 62.
The second rectifier 80 is coupled to the transformer via the second winding 28 wherein the second winding 28 is coupled to the fourth diode 34 and the second freewheeling diode 46. The second freewheeling diode 46 is coupled to the second inductor 44 and the third capacitor 52. The switch 20 is coupled to a driver 16 wherein the driver 16 is coupled a pulse width modulator 22. The pulse width modulator 22 is coupled to the optocoupler 36 wherein the optocoupler 36 is coupled to the third resistor 37. The third resistor 37 is coupled to the second error amplifier 48 wherein the second error amplifier 48 is coupled to the third resistor 54 and the fourth resistor 56.
The input voltage 10 is switched on and off at a very high frequency via the primary winding 4-6 of transformer 18 and switch 20. The switch 20 is switched on and off by the pulse width modulator 22 and the driver 16. The primary energy is transformed to the rectifiers 70, 80 by means of the first and second windings 26, 28. Consequently, a main output voltage 66 is obtained by rectifying the switched voltage developed across the second winding 28 with the fourth diode 34 and the second freewheeling diode 46. The rectified voltage is then averaged by the second inductor 44 and the third capacitor 52 thereby producing the main output voltage 66. Furthermore, the main output voltage 66 is regulated by a feedback loop comprising the second error amplifier 48, the optocoupler 36 and the pulse width modulator 22.
Similarly, a second output voltage 64 is obtained by rectifying the switched voltage developed across the first winding 26 with the third diode 32 and the first freewheeling diode 42. The rectified voltage is then averaged by the first inductor 40 and the second capacitor 50 thereby producing the second output voltage 64. The second output voltage 64 is regulated by modulating the switched voltage developed across the first winding 26 with the MAGAMP core 24, the MAGAMP driver 38, and the first error amplifier 62.
The transformer 18 is chosen whereby the duty ratio of forward energy transfer is close to 25%. This is done to provide regulated outputs for 20 ms interruptions of the AC line voltage. Because the forward energy is transferred 25% of the time, the third diode 32 and the fourth diode 34 are conducting the current for 25% of the time. Consequently, the first freewheeling diode 42 and the second freewheeling diode 46 are conducting the current for the remaining 75% of the time. Because power is dissipated when the diodes are conducting current, power is dissipated for 75% of the time while the freewheeling diodes 42, 46 are conducting the current. This dissipation of power significantly reduces the overall efficiency of the conventional multiple output power supply circuit.
Accordingly, what is needed is a more efficient multiple output power supply circuit. The circuit should be simple, cost effective and capable of being easily adapted to current technology. The present invention addresses such a need.
A multiple output power supply circuit is disclosed. The power supply circuit comprises an input voltage wherein the input voltage is coupled to a driver and a transformer coupled to the input voltage wherein the transformer is coupled to at least one switch. The power supply circuit further comprises at least two rectifiers, each of the at least two rectifiers coupled to the transformer via a winding, each of the at least two rectifiers comprising at least one diode and a controlled switching device coupled in parallel.
According to the present invention, the circuit in accordance with the present invention provides multiple power outputs in a substantially more efficient manner.